Thermostat apparatus



Feb. 12, 1963 N. H. DE NEVERS 3,077,112

THERMOSTAT APPARATUS Filed Nov. 27, 1961 mcaoswnca-r E; wcRoswncH a: M ,J v

I 3 i5 V \3 4 i! w: y A 6 N Z Z FIG-3 M INVENTOR N01. H. 05 EV 3,077,112 THERMQr STAT APPARATUS Noel H. de Nevers, San Rafael, Calill, assignor to California Research Corporation, dan Francisco, Cali, a corporation of Delaware Filed Nov. 27, idol, der. No. 155,141

ll Claims. (Cl. 73-45635) This invention relates to thermostats, and more particularly to derivative action thermostats capable of compensating for the lag between the time when a change occurs in the heat output from a heat source and the time when the temperature of the atmosphere surrounding the thermostat reaches equilibrium after changing in response to said change in heat output.

Particularly in modern residential construction, simple existing thermostats do not compensate for time lags of the aforesaid type. Existing residence thermostats generally are of the simple on-ofi? type. Such on-oil thermostats are particularly unsatisfactory with such heating systems as radiant heating systems located in floor slabs, because of the long interval between the time of turning on or oil the furnace and the time when the temperature of the atmosphere being controlled by the thermostat reaches equilibrium. Thermostats capable of compensating for this time interval heretofore generally have been too complex and expensive to be of practical applicability to residential construction.

it is an object or the present invention to provide a simple, dependable, positive-action, and trouble-free ther- .mostat capable of compensating for such time lags and particularly suitable for use in residential construction.

in accordance with the present invention, there is provided a thermostat comprising a bimetallic strip having a substantially fiat elongated first metal strip member of a first metal having a relatively low coetlicient of expansion, an uninsulated second elongated metal strip member of a metal different from said first member and shorter than said first member and having a higher coefiicient of expansion than said first member and aligned with and secured to one side of said first member with one end of said second member near one end of said first member, a third elongated metal strip member of a metal difierent from said first member and shorter than said first member and havin a higher coefficieut of expansion than said first member and aligned wtih and secured to the other side of said first member near the other end of said first member, insulation substantially surrounding said third member and that portion of said first member in contact with said third member, and a substantially flat base plate secured to the adjacent ends or" said first member and said third member with one side of said base plate at substantially right angles to the longitudinal axis of said bimetallic strip, whereby a change in temperature of the atmosphere in which said bimetallic strip is located will cause the temperature of said uninsulated second strip member to change more rapidly than the temperature of said insulated third strip member.

T he invention will best be understood, and further objects and advantages thereof will be apparent, from the following description when read in connection with the accompanying drawings, in which:

FIG. 1 is a sectional elevation view illustrating the main elements of an embodiment of the thermostat of the present invention;

FIG. 2 is a sectional elevation view illustrating a modification of the apparatus shown in FIG. 1;

PEG. 3 is a sectional elevation view illustrating the main elements of a further embodiment of the thermostat of the present invention; and

FIG. 4- is a sectional elevation view illustrating a modification of the apparatus shown in FIG. 3.

Referring now to FIG. 1, a fiat elongated first metal strip member 1, having a relatively low coeiiicient of expansion, which may be iron for example, is secured at one end to a base plate 2, which may be of iron, brass or other suitable material. Shorter flat elongated metal strip members 3 and 4 having a higher coefiicient of expansion than member 1 are firmly secured to member 1, for example by riveting, in the locations shown. A flexible in sulating material 5, for example fiberglass or rubber, sur rounds member s and the lower portion of member 1, as shown. Base plate 2 desirably is hinged to an adjacent structure, for example a container for the thermostat apparatus, by means or" a hinge 6. Adjusting screw 7 is provided for adjusting the proximity of the adjacent ends of members 1 and 3 to microswitch 8, which is controlled by movement of said adjacent ends of members 1 and 3 into and out of contact with microswitch 8, which in turn controls a heat source such as a household furnace.

In a convenient construction of an embodiment of this invention for residential use, all three members 1, 3 and 4 may be metal strips about -inch to -inch thick and %-lI1Ch wide. Main metal strip member 1 with a relatively low coetficient of expansion may be constructed of a suitable material, such as iron. Metal strip members 3 and 5 may be constructed of suitable metals having higher coeflicients of expansion than that of member 1, for example brass. So long as members 3 and 4 both have higher coefiicients of expansion than main member 1, they may be different metals if desired.

The operation of the apparatus shown in FIG. 1 may be explained by assuming that the mechanism, including the bimetallic element and the microswitch, is normally closed at an equilibrium temperature below 70 F. AS- suming that the equilibrium temperature of the atmosphere surrounding the thermostat is 50 F. and that the term perature of this atmosphere rises rapidly in response to the output of a heat source such as a furnace, the temperature of uninsulated member 3 will rise faster than the temperature of insulated member 4-; accordingly, when the temperature of member 3 is at 60 F. for example, the temperature of member 4 will be only at 50 F., for example. Under such circumstances, with the mechanism properly adjusted, the switch will open in response to the preponderating stresses set up in the mechanism because ember 3 has expanded more per unit length than member 4, whereas the switch would not be open at all at a temperature of 60 F. were that the equilibrium temperature of the surrounding atmosphere. 'I.e., if members 3 and 4 both were at 60 F., or any temperature up to 70 F the switch would be closed.

A similar action in the reverse direction occurs when the switch is open and the temperature drops rapidly. For example, it may be assumed that the equilibrium temperature of the surrounding'atmosphere is 90 P. so that the switch is open, and that the temperature drops rapidly from that value. In this case, uninsulated member 3 will cool faster than insulated member 4. When member 3 is at F. for example, and member 4 is at F., the preponderating stresses caused by the greater contraction per unit length of member 3 than that of niember 4 will cause the switch to close, despite the fact that the switch would be open at a surrounding equilibrium temperature of as low as about 70 F.

Referring now to PEG. 2, there shown is a modification in the construction of the embodiment of the present invention shown in FIG. 1. In the construction shown in FIG. 2, the main strip member 1 is bent as shown, which enables the insulation material 5 to be movable, so that the thermal response characteristics of the thermostat may be varied. By making the insulation movable, it is possible to control not only the set point of the apparatus, which is controlled by adjusting screw 7, but it is also possible to control the amount of derivative action accomplished by the mechanism. Sliding the insulation upwardly decreases the derivative action. However, obviously, the insulation should not be raised to the point where there is no derivative action or that the derivative action becomes negative.

Referring now to FIG. 3, there shown is a sectional elevation view illustrating the main elements of an embodiment of the thermostat of the present invention wherein improve action is obtained by positioning the insulation as shown, surrounding member 3 and the upper portion of member 1. By positioning insulation 5 in this manner, uninsulated member 4 heats and cools faster than insulated member 3, and microswitch 8 is placed in the location shown, for activation by contact with insulation 5. 'It will be noted that member 3 is less affected by heat transfer from base plate 2 than is insulated member 3 in the embodiment shown in FIG. 1; accordingly, the embodiment of FIG. 3 tends to be more sensitive and more positive in action.

Referring now to FIG. 4, there shown is a modification in the construction of the embodiment of the present invention shown in FIG. 3. In the construction shown in FIG. 4, the main strip member 1 is bent as shown, which enables the insulation material 5 to be movable, so that the thermal response characteristics of the thermostat may be varied. By making the insulation movable, it is possible to control not only the set point of the apparatus, which is controlled by adjusting screw 7, but it is also possible to control the amount of derivative action accomplished by the mechanism. Sliding the insulation downwardly decreases the derivative action. However, obviously the insulation should not be lowered to the point where there is no derivative action or that the derivative action becomes negative.

From the foregoing, it may be seen that the apparatus of the present invention provides an extremely simple, steady, dependable thermostat of the bimetallic strip type having a positive derivative action to compensate for the time lag between the time when the heat output of a heat source changes and the time when the temperature of the atmosphere heated by the heat source reaches an equilibrium. While the aforesaid description covers only particular embodiments of the apparatus of the presentinvention, it will be apparent to those skilled in the art that numerous changes and modifications in this apparatus may be made without departing from the spirit of the invention, and all such changes are intended to be included within the scope of the present claims.

I claim: s

1. A thermostat comprising a bimetallic strip having a substantiallyfiat elongated first metal strip member of a first metal having a relatively low coefiicient of expansion, a second elongated metal strip member of a metal different from said first member and shorter than said first member and having a higher coefiicient of expansion than said first member and aligned with and secured to one side of said first member with one end of said second member near one end of said first member, a third elongated metal strip member of a metal different from said first member and shorter than said first member and having a higher coefficient of expansion than said first memmetallic strip, whereby a change in temperature of the atmosphere in which said bimetallic strip is located will cause the temperature of the uninsulated shorter strip member to change more rapidly than the temperature of the insulated shorter strip member.

2. A thermostat as in claim 1, wherein said first strip member consists essentially of iron, and wherein said second and third strip members consist essentially of brass.

3. A thermostat as in claim 1, whereinsaid insulation substantially surrounding one of said second and third members and that portion of said first member in contact therewith is slidable on the surrounded members with respect to said base plate to vary the thermal response characteristics of said thermostat.

4. A thermostat as in claim 1, wherein said insulation substantially surrounds said second member and that portion of said first member in contact therewith.

5. A thermostat as in claim 1, wherein said insulation substantially surrounds said third member and that portion of said first member in contact therewith.

6. 'A thermostat comprising a bimetallic strip comprising a first elongated metal center strip member, a second and shorter elongated metal strip member having a higher coefficient of expansion than said first member and secured along the length thereof to one side of said first member near one end of said first member, a third elongated metal strip member shorter than said first strip member and having a higher coefficient of expansion than said first member and secured along the length thereof to the other side of'said first member near the other end of said first member, insulation substantially surrounding said third member and that portion of said first member in contact therewith, the adjacent ends of said first and third members being securely held by a sub stantially fiat base plate positioned with the top surface of said base plate substantially at right angles to the longitudinal axis of said bimetallic strip, whereby a change in temperature of the atmosphere in which said bimetallic strip is located will cause the temperature of said uninsulated second strip member to change more rapidly than the temperature of said insulated third strip member to produce a movement of the unsecured end of said bimetallic strip with respect to said base plate and with respect to a switch to cause operation of the mech-; anism of said switch in response to said movement.

7. A thermostat as in claim 6, wherein said first strip. member consists essentially of iron, and wherein said second and third strip members consist essentially of brass.

8. A thermostat as in claim 6, wherein said insulation 7 substantially surrounding said third member and that portion of said first member in contact with said third member is slidable on said first and third members with respect to said base plate to vary the thermal response characteristics of said thermostat.

9. A thermostat comprising a bimetallic strip comprising 'a first elongated metal center strip member, a second and shorter elongated metal strip member having a higher coefficient of expansion than "said first member and secured along the length thereof to one side of said first member near one end ofsaid first member, a third elongated metal strip member shorter than said first strip member and having a higher coefficient of expansion than said first member and secured along the length thereof'to the other side of said first member near the other end of said first member, insulation substantially surrounding said second member and that portion of said first member in contact therewith, the adjacent ends of said first and third members being securely held by a substantially fiat base plate positioned with the top surface of said base plate substantially at right angles to the longitudinal axis of said bimetallic strip, whereby a change in temperature of the atmosphere in which said bimetallic strip is located will cause the temperature of said uninsulated third strip member to change more rapidly than the temperature of said insulated second strip member to produce a movement of the unsecured end of said bimetallic strip with respect to said base 6 substantially surrounding said second member and that portion of said first member in contact with said second member is slidable on said first and second members with respect to said base plate to vary the thermal response characteristics of said thermostat.

No references cited. 

1. A THERMOSTAT COMPRISING A BIMETALLIC STRIP HAVING A SUBSTANTIALLY FLAT ELONGATED FIRST METAL STRIP MEMBER OF A FIRST METAL HAVING A RELATIVELY LOW COEFFICIENT OF EXPANSION, A SECOND ELONGATED METAL STRIP MEMBER OF A METAL DIFFERENT FROM SAID FIRST MEMBER AND SHORTER THAN SAID FIRST MEMBER AND HAVING A HIGHER COEFFICIENT OF EXPANSION THAN SAID FIRST MEMBER AND ALIGNED WITH AND SECURED TO ONE SIDE OF SAID FIRST MEMBER WITH ONE END OF SAID SECOND MEMBER NEAR ONE END OF SAID FIRST MEMBER, A THIRD ELONGATED METAL STRIP MEMBER OF A METAL DIFFERENT FROM SAID FIRST MEMBER AND SHORTER THAN SAID FIRST MEMBER AND HAVING A HIGHER COEFFICIENT OF EXPANSION THAN SAID FIRST MEMBER AND ALIGNED WITH AND SECURED TO THE OTHER SIDE OF SAID FIRST MEMBER NEAR THE OTHER END OF SAID FIRST MEMBER, INSULATION SUBSTANTIALLY SURROUNDING ONE OF SAID SECOND AND THIRD MEMBERS AND THAT PORTION OF SAID FIRST MEMBER IN CONTACT THEREWITH, AND A SUBSTANTIALLY FLAT BASE PLATE SECURED TO THE ADJACENT ENDS OF SAID FIRST MEMBER AND SAID THIRD MEMBER WITH ONE SIDE OF SAID BASE PLATE AT SUBSTANTIALLY RIGHT ANGLES TO THE LONGITUDINAL AXIS OF SAID BIMETALLIC STRIP, WHEREBY A CHANGE IN TEMPERATURE OF THE ATMOSPHERE IN WHICH SAID BIMETALLIC STRIP IS LOCATED WILL CAUSE THE TEMPERATURE OF THE UNINSULATED SHORTER STRIP MEMBER TO CHANGE MORE RAPIDLY THAN THE TEMPERATURE OF THE INSULATED SHORTER STRIP MEMBER. 